This invention relates to a shield tunnelling system capable of electromagnetically detecting conditions of ground near a cutter head of a shield tunneling machine.
Shield tunneling machines are utilized for constructions of underground facilities, e.g., railways, highways, water-works, sewers, power supply, etc., and are generally classified into open-faced and closed-face types mainly according to whether an operator of the shield tunneling machine is able to watch a cutting face by sight, or not.
One important factor necessary in shield tunneling is to stabilize the cutting face. Especially while excavating under special working conditions, such as in a sand layer having a small uniform coefficient or a lamination of certain number of layers having different properties, the ground near the cutting face is liable to collapse. Since cave-ins formed as a result of collapse should be filled with a filling material for preventing a local sinking of the ground surface, it is important to detect the collapse immediately and continuously.
Compared with the open-face shield tunneling machine, the closed-face shield tunneling machine has a higher degree of the cutting face stability but has the disadvantage in that the operator thereof is unable to measure the collapse of the ground by sight.
A method for detecting or supervising the existence of the cave-ins near the cutting face by using electromagnetic impulse is disclosed in Japanese Laid Open Patent Specification No. 18199 of 1983. According to this method, the electromagnetic impulse is radiated from a transmitter antenna installed on the top of the skin plate of the shield tunneling machine and some of the electromagnetic wave energy is reflected at the interface between materials of different electrical properties and is received by a receiver antenna so as to detect the condition of the cutting face or especially the existence of the the cave-ins based on the wave shape and intensity of the received electromagnetic waves thereby confirming cave-ins of the ground and the range of the earth loosening caused by the collapse. However, it has been impossible to correctly know the size and shape of the cave-ins and the degree of loosening. Furthermore, no practical method has been available for mounting the transmitter and receiver antenna on the shield tunneling machine.